Ah, DNA!

The first half of the 20th century saw rapid growth of understanding of gene transmission; the second half has seen the development of our understanding of the actual nature of genes, and the ways in which their messages are expressed. This, of course, is the science of DNA: Molecular Genetics.

DNA From our millennial perspective, it is difficult to remember that it has been less than 50 years since the publication of James Watson and Frances Crick's paper revealing the structure of DNA. It has only been a few years longer since it was actually established that DNA is what genes are made of. Since the 1950s, our knowledge and understanding of DNA have exploded.

The study of DNA and its functions can be very complex and technical — it is an extremely large molecule, and its functions are the intricate and complicated functions of large molecule chemistry. But a lot of the important things we understand about DNA aren't complicated. They are elegant and beautiful in their simplicity.

DNA is an information bearing molecule — a language molecule. It is constructed out of very long chains of four different small composite molecules, and the order of these four molecules determines the message coded into the molecule, just as the order of letters in a word determines the meaning of the word. If this weren't impressive enough, each of these extremely long chains fits precisely against a partner chain in such a way that each of them precisely complements the order of the four components its partner. Because of this aspect of DNA, each molecule can split its two chains apart and build a new matching strand for each — thus duplicating the original molecule. Every time a cell's nucleus goes through mitosis or meiosis, the DNA in the chromosomes of that nucleus must first complete this copying process to produce the two copies of each chromosome necessary for the daughter nuclei.

Of course, DNA doesn't exist simply for the purpose of making copies of itself. Its real task is to carry the instructions necessary for building and running the cell — and the organism of which the cell may be a part. The DNA of a human cell carries about 30,000 different genes. Each of these genes is a set of instructions — a recipe, if you will — for the production of a specific protein. And the 30,000 or so proteins a human's cells can make determine all of the hereditary features of that human. You are what your proteins say you are (except, of course, for the influence of environment).

The process by which the instructions in a DNA molecule are read and followed is one of the most amazing phenomena of life. It involves a third kind of molecule called RNA, and the activity of the cell's army of ribosomes. These three components — DNA, RNA and ribosomes — interact in an intricate dance which manufactures the proteins which directly or indirectly perform all of the functions of life.

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Updated 25 September 2004